This invention relates to conduits which indicate if a leak is present therein and more particularly to leak indicating flexible bellows used as expansion joints.
It is known to connect the adjacent ends of aligned pipes by means of a flexible bellows to accommodate the expansion and contraction of the pipes at the joint. Such joints are typically formed of a corrugated composite metal conduit comprising an inner tube and a coaxial outer tube spaced from the inner tube. In order that the metal conduit may be flexible, the inner and outer tubes are necessarily relatively thin. Since the fluids carried by the pipes may be toxic or explosive, and may be valuable as well, it is important to be able to detect a leak in the expansion joint and to detect the possibility of a joint failure before it occurs.
Some conduits designed to indicate the presence of leaks are currently known. For example, U.S. Pat. No. 3,183,022 to Sayag discloses a two-ply expansion joint in which the space between the plies is sealed off. A coupling is provided in communication with the space so that a device which is capable of detecting the flow of fluid within the joint may be connected thereto. Thus, the detecting device can periodically be hooked up to the coupling to check for leaks in the inner ply of the expansion joint.
U.S. Pat. No. 3,232,640 to Donkle discloses a two-ply corrugated expansion joint in which a space between the plies is filled with a fluid exerting superatmospheric pressure or is evacuated. A connector is provided in communication with the space so that a leak detecting apparatus can be attached thereto to check for leaks in the inner ply and the outer ply.
U.S. Pat. No. 3,299,417 to Sibthorpe discloses a flexible tube having an inner ply and an outer ply with a space between the plies. An expansible bellows is mounted in communication with the space and an indicating button is supported on the bellows below a horizontal panel. The space is evacuated so that the bellows and the button are maintained in a lower position in which the indicating button is concealed. A spring biases the button into the concealed position. Thus, if a break occurs in the inner ply, the pressure of the fluid being conveyed through the flexible tube will enter the space between the inner and outer plies and flow into the expansible bellows to force the button up against the bias of the spring into a visible position, thereby giving an indication of a leak in the inner ply. The indicating button may be arranged to operate an electrical switch to provide an additional signal, supplementing the signal which is provided by the movement of the button itself.
Although the foregoing patents represent improvements in the art of flexible conduits, the prior art fails to provide a leak indicating conduit which includes a mechanism for continuously monitoring both the inner ply and the outer ply for a leak and for giving an immediate leak signal in response to a leak in either the inner ply or the outer ply. In addition, where the flexible conduit is employed as an expansion joint between two pipes, the prior art fails to provide an arrangement for indicating leaks at the connections between the flexible conduits and the pipes.